Pawing can be a sign of boredom, stress or anger, which can be all tied in with frustration to some extent, being a repetitive behaviour.
I've managed to almost eradicate constant pawing while being hard fed in one of my horses, but her reasons for pawing, were more specific than in the case of your horse. As the behaviour was limited to feeding, I was able to set up ways to stop it.
Horses require little sleep compared to humans. They get most of this rest dozing while standing, but only require 30 minutes of deep sleep only obtained while lying down. These shorter sleep requirements mean that the horse is awake for longer and so boredom while being stalled is an issue.
It's important though to acknowledge that it's unlikely to be only boredom that is causing this behaviour. It is likely there is a level of stress also associated with the pawing, as she is kept away from other herd animals. A stall is isolated, and small. It can be stressful to be locked in such a small space for prolonged periods, despite this being an acceptable practice. The fact there's so few problems with horses being stalled is due to their submissive nature rather than the fact it is beneficial to them or that they enjoy it.
The ideal solution is to leave horses in pasture 24/7, but they do not do well alone. Being herd animals and prey animals, they rely on other horses to watch over them while they sleep.
Horses night vision is excellent, so a vision impaired horse left in a paddock over night that they are used to and in during the day should not be a problem for that horse. Of course any hazards should be removed, but this is the case for all horses.
Pawing at the concrete will damage her hooves. One way around that would be to remove the bedding and lay thick rubber matting over the concrete and then lay the bedding over that.
She is your horse and you are there and know her, you may find that leaving her in the pasture overnight alone is preferable for her health. As mentioned in your post and this answer, they like company, so at least in a stall she has horses near her.
If there is anyway to put her in a paddock that is near the stalls, that would be better. Or even let the vision impaired horse into a yard at night next to the paddock. This may not be feasible, but are just ideas.
Pawing. Horses paw—an arcing action with the foreleg that may dig a trench in soft ground—for a number of reasons. The bored or
impatient horse paws when tied—he's saying that he's tired of standing
around and he's ready to go! Stressed horses may paw in the
trailer or at feeding time, and the behavior stops when the source
of the anxiety is past.
The issue with pawing is that by preventing the actual pawing, without dealing with the underlying issue, may indeed cause other behaviours that are destructive for the horse and possibly you.
From Stereotypic Behaviors in the MSD Veterinary Manual
Pawing or digging can cause injury to the horse, damage the floor, and cause wear to the horse’s hooves. It is a normal behavior when
horses on winter pasture are forced to dig for feed. When horses are
confined and fed highly palatable foods, pawing can occur more
frequently and more intensely than it would otherwise. Pawing can
occur due to frustration, anticipation, or as a displacement behavior.
The underlying cause of the pawing needs to be determined in order to
successfully treat it. Specific treatments are similar to those for
stall walking (see above). Changing the floors to concrete may stop
pawing; however, it will not change the motivation to do so, and some
horses (especially stallions) may rear up instead of pawing. Pawing
should not be rewarded, which is what inadvertently happens when
horses paw in anticipation of feeding. The food should be presented to
the horse only when the horse is not pawing, or the horse should be
brought to the food.
And
Stall walking or circling is a stereotypical behavior in which horses walk in circles around the stall. When released to a larger
space (such as a pasture or barn), they continue to circle in a small
area. Tying the horse to prevent walking will only transform the
behavior into weaving (see below). Both behaviors are seen in confined
horses, serve no purpose, are hard to interrupt, and are usually
slower than other types of movements. Possible causes of stall walking
include lack of exercise and social contact and claustrophobia (an
intense fear of small spaces). Stress and anxiety appear to make the
problem worse. Treatment should include increasing exercise, providing
social company, allowing the horse to see other horses, and providing
clean, thick bedding. Feeding frequently (more than twice daily),
allowing more access to pasture, providing more open stalls, and
providing better access to outside views can also help. Adding toys to
the stall may help if the horse is young and active. In some cases,
your veterinarian may need to prescribe medication to control the
problem.
